London -LRB- CNN -RRB- -- It 's not unusual for a visiting head of state to lay a wreath at the Tomb of the Unknown Warrior in London 's Westminster Abbey -- but when it happens on Tuesday , the gesture will be anything but routine . This is history in the making .

The commemoration by the President of Ireland , Michael D. Higgins , will take place during the first state visit by an Irish leader to the United Kingdom . It follows on from Queen Elizabeth 's trip to Dublin in May 2011 , the first by a British monarch to the republic since it gained independence from London in 1921 .

The countries are close neighbors but have a long , contentious , often violent history which has left thousands dead , among them Lord Mountbatten , a relative of the Queen who was killed by an Irish Republican Army -LRB- IRA -RRB- bomb in 1979 . The very fact that the British and the Irish once fought with each other under the same flag is still very difficult for many Irish Republicans to stomach .

But the relationship between the two countries has gradually normalized since the peace process of the 1990s . That will be formally acknowledged when Higgins pays his respects at the tomb of an unknown British soldier who died during World War One when Ireland was under British rule .

Diplomats from both countries are stressing the significance of the five-day trip . Dan Mulhall , the Irish Ambassador to London , has said that Dublin is `` now willing to look at the facts of history '' rather than shying away from them .

Meanwhile a Foreign and Commonwealth Office spokesperson has said that the visit is about acknowledging the past but also `` demonstrating that the relationship is moving on and looking to the future . '' The spokesperson stressed that both state visits are `` pivotal moments in our shared history . ''

The Queen 's trip nearly three years ago included a visit to Croke Park , a Dublin sports stadium where 14 people were killed by British forces in 1920 during the war of independence .

She also spoke in Gaelic during a dinner in Dublin to audible gasps in the room ; and visited Northern Ireland in June 2012 , when she shook hands with former IRA commander Martin McGuinness , now the province 's deputy first minister .

These were all highly symbolic moments that politicians could n't create to the same effect -- and Buckingham Palace is well aware of that . A palace spokesperson said last month that the Queen herself has become a symbol of the warming relationship between the two countries .

The significance of this week 's state visit will be further underlined by the presence of McGuinness at a reception hosted by the Queen on Thursday afternoon at Windsor Castle - a move unthinkable only a decade ago .

The palace spokesperson confirmed that the Queen is heavily invested in the state visit and that it is personal for her , adding that `` the Queen is across every detail . ''

Expect the Irish President to have everything laid on for him , with all the pomp and ceremony that the royal household can muster .

Tensions still remain in Northern Ireland : while the bloodshed of previous decades has largely stopped there are still occasional incidents which pose a threat to life and tensions remain between the communities .

But Anglo-Irish relations are improving with each symbolic moment -- and this week 's state visit is as symbolic as it gets .

READ : Mary Robinson : Finally , Britain and Ireland are reconciled

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Visit of Irish president marks first state trip to London since 1921

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Queen Elizabeth made historic visit to Dublin nearly three years ago

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Foster : Relations between two countries have gradually normalized since 1990s